A 62-year-old woman was admitted for nephrotic syndrome and lung tumor. A renal biopsy showed membranous features of the glomeruli. Immunofluorescence studies revealed granular IgG4-κ deposits along with the glomerular basement membrane. Electron microscopy revealed granular electron-dense deposits. Further study denied multiple myeloma. Light microscopy of the resected lung tumor revealed IgG4-related lung disease with no malignancy. Steroid therapy induced a remission of the nephrotic syndrome, with no recurrence of the lung tumor. We consider that this is the first case of a proliferative glomerulonephritis with monoclonal IgG deposits of IgG4 subclass, and a rare concurrence with IgG4-related disease.